Transport protein which effects the transport of cationic xenobiotics and/or pharmaceuticals, DNA sequences encoding it and their use

ABSTRACT

A transport protein has been cloned which is present in liver epithelial cells and kidney epithelial cells and in intestinal cells and is responsible for transporting cationic pharmaceuticals and/or xenobiotics. This transport protein has been described more specifically by its DNA and amino acid sequences, and various uses are disclosed which are, in particular, of great importance for developing novel medicaments.

This application is a division of application Ser. No. 08/501,572, filed Jul. 12, 1995, now allowed, which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

In mammals, and in humans in particular, cationic pharmaceuticals and xenobiotics of varying molecular structure, catecholamines and other endogenous cations are excreted in the kidney and liver by polyspecific transport proteins which are located in luminal and basolateral plasma membranes. These transport proteins differ, as regards their function, from the previously known monoamine transport proteins in neuronal plasma membranes and synaptic vesicles and from the ATP-dependent proteins for exporting hydrophobic pharmaceuticals (multidrug transport proteins).

Within the scope of the present invention, a complementary DNA sequence was initially isolated from rat kidneys, which sequence encodes a membrane protein of 556 amino acids in length and is designated OCT1 in that which follows. This transport protein acts in the basolateral membrane of the proximal renal tubules and in hepatocytes as a cation transporter for various target molecules.

The transport protein designated OCT1 is not homologous with any other previously known protein, exhibits a thus far unique distribution of hydrophobic and negatively charged amino acids and is found exclusively in kidneys, the liver and intestine. The OCT1 transport protein transports cations of varying structure, is inhibited by a large number of cationic substances of differing hydrophobicity and possesses functional properties which differ from those of a previously known polyspecific transport protein (multidrug transporter), which is only able to transport very hydrophobic substances. The transport protein OCT1 is regarded as a new prototype of a polyspecific transport protein in mammals.

Many organic cations, including frequently used pharmaceuticals such as antihistamines, antiarrhythmics, sedatives, opiates, diuretics, cytostatic agents and antibiotics, are excreted into the urine and into the bile by means of being actively transported through kidney epithelial cells and hepatocytes. When being actively secreted in the kidney, the cations are transported by polyspecific transport systems in the basolateral and luminal plasma membranes of the proximal renal tubules. The two systems differ as regards their function. The transport proteins in the basolateral membrane, which are able to transport structurally different cations such as tetraethylammonium (TEA), N'-methylnicotinamide (NMN) and N-methyl-4-phenylpyridinium (MPP), are inhibited by a large number of extracellular cations of differing structure. These transport proteins can be driven by a membrane potential which is internally negative and by the oppositely directed transport of intracellular substrates. Two transport systems have been described in the luminal membrane which, while being driven by an outwardly directed proton gradient, are not affected by the membrane potential. One of these transport systems has a broad substrate specificity which is comparable to that of the cation transport system in the basolateral membrane of proximal renal tubules. Owing to functional similarities, it is assumed that this polyspecific transport system in the luminal membrane is identical to the extraneuronal transport system for noradrenalin in the heart.

SUMMARY OF THE INVENTION

The present invention therefore relates to transport proteins which are responsible for transporting cationic xenobiotics and/or pharmaceuticals from the blood into the epithelial cells of the liver or kidney or for transporting cationic xenobiotics or pharmaceuticals from the intestine into the blood circulation.

The novel transport proteins exhibit a constituent sequence of at least seven amino acids selected from the amino acid sequence which is depicted in FIG. 2a₁ (SEQ ID NO:1), FIG. 2a₂ (SEQ ID NO:2) or FIG. 2a₃ (SEQ ID NO:3). In a preferred embodiment, the constituent sequence from FIG. 2a₁ (SEQ ID NO:1), FIG. 2a₂ (SEQ ID NO:2) or FIG. 2a₃ (SEQ ID NO:3) has a length of at least 10 amino acids and, in a particularly preferred embodiment, a length of at least 14 amino acids.

The present invention also relates to DNA sequences which encode a novel transport protein. The novel DNA sequences exhibit a constituent sequence of at least 21 bases selected from the sequence shown in FIGS. 2a₁ (SEQ ID NO:4), 2a₂ (SEQ ID NO:5) or 2a₃ (SEQ ID NO:6). In a particularly preferred embodiment, the constituent sequence has a length of at least 30 bases and, in a very particularly preferred embodiment, of at least 42 bases.

The novel transport proteins and DNA sequences are of particular importance in medical and pharmacological research. The novel DNA sequences can be used, for example, to prepare epithelial cell lines which permanently express a novel transport protein. For this purpose, the DNA sequence encoding the transport protein is incorporated, using genetic manipulation methods which are known per se, into a suitable vector, which is used to transform a suitable epithelial cell line which did not previously express the transport protein. In this way, cell lines can be obtained which constantly express a novel transport protein.

Epithelial cell lines of this nature, which express the transport proteins, can be employed in vitro to test the renal and biliary excretion, and also the intestinal absorption, of cationic pharmaceuticals and/or xenobiotics which are to be expected. Thus, such cell lines can be used to determine at the in vitro stage, that is without elaborate animal experiments, whether and if so to what extent pharmaceuticals, and other biologically active compounds as well, are excreted or absorbed from the intestine into the blood circulation.

The novel DNA sequences can be used to isolate those transport proteins which are homologous with the novel transport proteins. The corresponding transport proteins which are homologous with the transport proteins disclosed in accordance with the invention can therefore be isolated from all mammalian species and from humans. Two corresponding human sequences have already been determined. One possible means of effecting such an isolation is to use the now well known polymerase chain reaction. To do this, it is only necessary to select suitable DNA sequences from the sequence shown in FIG. 2a₁ (SEQ ID NO:4), 2a₂ (SEQ ID NO:5) or 2a₃ (SEQ ID NO:6) which can serve as primers for the polymerase chain reaction. These primers can be used to isolate homologous transport proteins without difficulty.

A further possible use of the novel transport proteins and/or of the novel epithelial cell lines is to develop cationic signal molecules which can be attached to biologically active compounds, such as pharmaceuticals, in order to alter their renal and biliary excretion or their intestinal absorption. In this way it is possible to examine different chemical structures to see whether they favor excretion via the kidney or the liver of the molecule to which they are linked, and also promote absorption from the intestine into the blood circulation, or whether they bring about the opposite effect in each case.

The novel transport proteins can also be employed, in particular, for generating antibodies, in particular monoclonal antibodies, which can be used to block the uptake of pharmaceuticals into renal tubule cells in order to decrease the nephrotoxicity of cationic pharmaceuticals.

Furthermore, the disclosure of the invention can be used as the basis for developing specific pharmaceuticals which affect the excretion of certain other cationic pharmaceuticals and/or xenobiotics. In this way it is possible to develop pharmacologically active substances which are able to influence the uptake of other active compounds. An influence of this nature can either comprise promoting or preventing uptake of an active compound from the intestine or promoting or preventing excretion of an active compound in the kidney and liver.

An additional preferred use of the novel DNA sequences is that of developing antisense nucleotide sequences. In this context, nucleotide sequences can be developed which prevent transcription and/or translation of the corresponding genes by binding to the corresponding, naturally occurring, complementary nucleotide sequences.

An additional preferred use of the novel DNA sequences is their use in molecular test kits for diagnosing molecular defects at the genome level in renal and/or biliary cation excretion mechanisms. In molecular test kits of this nature, the DNA sequences can be used, in a particularly preferred embodiment, for carrying out the polymerase chain reaction. In this case, the known DNA sequence is used as the basis for selecting and synthesizing primer sequences which can then be employed in the polymerase chain reaction to amplify the gene from the respective patient which encodes the cation transporter and to examine this gene for genetic mutations.

DETAILED DESCRIPTION OF THE INVENTION

The nature of the present invention is explained in more detail with the aid of the following examples which are not, however, intended to limit the invention.

EXAMPLE 1

In order to clone the genes encoding the transport protein, blunt-ended double-stranded cDNA was firstly prepared from rat kidney poly(A)⁺ RNA using a NotI oligo(dT) primer for synthesizing the first strand. Once EcoRI adaptors containing an SP6 RNA polymerase promoter had been attached to the cDNA, the latter was digested with NotI and the resulting fragments were size-fractionated (1.5 to 2.3 kb) and inserted into the EcoRI restriction site of the vector pBluescript (stratagene); the recombinant vector was then electroporated into the E. coli strain DH10B. The plasmid DNA was isolated from pools of transformants, linearized with NotI and transcribed using the SP6 RNA polymerase.

The cRNA was purified by means of poly(A)⁺ selection and injected at a concentration of from 20 to 40 ng per oocyte. The oocytes were incubated and the NMN-inhibitable ¹⁴ C-TEA uptake was measured. Using a targeted screening method, a single clone, containing the gene encoding a kidney cation transporter, was isolated from the gene library. It was only possible to isolate this clone after having optimized and partially modified the methods which were used. In order to sequence the identified DNA, overlapping restriction fragments of OCT1 were subcloned and completely sequenced on both strands.

The OCT1 gene, which was isolated from a rat kidney gene bank and which comprised a cDNA fragment of 1882 base pairs in length, was expressed in Xenopus laevis oocytes. For this purpose, the oocytes were incubated, following RNA injection, for three days in 5 mM Hepes-Tris buffer, pH 7.5, 110 mM NaCl, 3 mM KCl, 2 mM CaCl₂, 1 MM MgCl₂ (designated ORi in that which follows). Transport was measured by incubating the oocytes with ¹⁴ C-TEA (tetraethylammonium) which was dissolved in ORi (22° C.). Furthermore, experiments were carried out using differing concentrations of Na⁺ and K⁺, as were experiments in the presence of Ba⁺⁺, at different pH values and in the presence of different inhibitors. Since, at the ¹⁴ C-TEA concentrations used, the uptake brought about by expressed OCT1 protein was linear in ORi buffer for more than 90 minutes, the uptake rates were determined after 90 minutes of incubation. When measurements were made with altered concentrations of Na⁺, K⁺ and H⁺ and in the presence of inhibitors, the oocytes were firstly incubated for 30 minutes under the appropriate buffer conditions and the uptake rates were then determined during a 30-minute period of incubation with ¹⁴ C-TEA. Following the incubation with ¹⁴ C-TEA, the uptake was terminated and the oocytes were washed and examined for the amount of radioactivity they had taken up.

Thus, the 1882 base pair cDNA fragment was expressed using Xenopus laevis oocytes (as described above); the OCT1 protein which was expressed in this way induced an uptake of ¹⁴ C-tetraethylammonium (¹⁴ C-TEA) which NMN (N¹ -methylnicotinamide) was able to inhibit, with the uptake being more than 250 times the values obtained in controls in which the oocytes were injected with water. The results are depicted graphically in FIG. 1a.

The cloned OCT1 cDNA contains an open reading frame which encodes a membrane protein having 556 amino acids. The amino acid sequence is depicted in FIG. 2a₁ (SEQ ID NO:1). It exhibits no similarities to the proteins in data banks.

The expression of ¹⁴ C-TEA uptake depended on the quantity of OCT1 cRNA that was injected. These results are presented FIG. 1b. The cRNA-dependence of the expressed uptake could be described by the Hill equation in which n=approximately 2.

The substance dependence of the ¹⁴ C-TEA uptake elicited by the OCT1 transport protein followed the Michaelis Menten equation. These results are depicted in FIG. 1c. The estimated K_(m) value of 95±μM was similar to the K_(m) value (160 μM) for cation transport through the basolateral membrane of rat proximal renal tubules which was determined in earlier experiments. It was 14 times lower than the apparent K_(m) value for the polyspecific H⁺ cation antiporter in the brush border membrane of rat proximal renal tubules.

EXAMPLE 2

In order to establish, in addition, whether the OCT1 transport protein represented the potential-dependent polyspecific cation transport system from the basolateral membrane or the potential-independent polyspecific H⁺ cation antiport system of the brush border membrane, tests were carried out to determine whether the uptake elicited by the OCT1 transport protein was dependent on the membrane potential or on a protein gradient across the membrane. The ability of different inhibitors to inhibit the expressed ¹⁴ C-TEA uptake was also investigated.

FIGS. 1d and 1e demonstrate that while the uptake of ¹⁴ C-TEA mediated by the OCT1 transport protein is dependent on the membrane potential, it is not altered appreciably when an inwardly directed or outwardly directed proton gradient of one pH unit is applied. The OCT1 transport protein therefore has the same basic characteristics as the cation transport measured across the basolateral membrane of the proximal renal tubules.

FIG. 1f and Table 1 demonstrate that the uptake of ¹⁴ C-TEA brought about by OCT1 is inhibited by organic cations of differing molecular structure. These structures include several frequently used pharmaceuticals such as quinine, desipramine, procainamide and O-methylisoprenaline. The estimated K_(i) values lie between 0.13 μM for 1-ethyl-2([1,4-dimethyl-2-phenyl-6-pyrimidinylidene]methyl)quinolinium chloride (cyanin 863) and 1 mM for tetramethylammonium (TMA).

                  TABLE 1                                                          ______________________________________                                          Inhibitor         K.sub.i (μM)                                             ______________________________________                                         Cyanine 863        0.13 ± 0.02                                                Decynium 22                    0.36 ± 0.08                                  Tetrapentylammonium           0.43 ±  0.09                                  Quinine                        0.93  ±  0.08                                Desipramine                   2.8 ± 0.6                                     Mepiperphenidol                5.2  ±  0.3                                  Procainamide                   13 ± 2                                       1-Methyl-4-phenylpyridinium    13 ± 2                                       Corticosterone                 >10                                             Reserpine                      >20                                             O-Methylisoprenaline           43 ± 5                                       Tetramethylammonium          1000 ± 100                                     N.sup.1 -Methylnicotinamide          1000 ± 200                           ______________________________________                                    

Table 1 shows the sensitivity of ¹⁴ C-TEA uptake in Xenopus laevis oocytes which were injected with the cRNA of the OCT1 renal transport protein.

When carrying out the inhibition experiments, the Xenopus laevis oocytes were injected with 5 ng of OCT1 cRNA and the effects of from 5 to 8 different concentrations of the inhibitors listed in Table 1 on the 95 μM uptake into the oocytes were measured. The values were also given in FIG. 1f. The inhibition curves were fitted by non-linear regression analysis and the K_(i) values (±SD) were determined.

In contrast to the previously known polyspecific transport protein, the so-called multidrug transporter, which is only inhibited by hydrophobic substances, the novel OCT1 transport protein was also inhibited by hydrophilic compounds such as TMA and NMN. Desipramine inhibited the transport elicited by OCT1 with a K_(i) value which was 700 fold greater than that with which it inhibited neuronal noradrenalin transport in plasma membranes of nerve cells. 5 μM reserpine has no effect on OCT1-elicited transport whereas the neuronal monoamine transport protein in synaptic vesicles is inhibited by sub-nanomolar concentrations of reserpine.

EXAMPLE 3

It was possible to confirm that the OCT1 transport protein was identical to the basolateral cationic transport protein by comparing the OCT1 K_(i) values with functional data which had previously been obtained from membrane vesicles and from measurements using cultured kidney epithelial cells. In making such a comparison, consideration has to be given to the species-dependent differences in cation transport and to the methodological limitations of the different methods for measuring inhibition of cation transport. In previous investigations, cation transport in rat kidneys was determined by microperfusion experiments which have to be carried out using short incubation times (4 seconds). Since it is not possible to use this method to determine diffusion-independent K_(i) values for high-affinity inhibitors, we have restricted ourselves to comparing low-affinity inhibitors. In a comparison of the low-affinity inhibitors TMA and NMN, we found that the K_(i) values for the OCT1-expressed transport protein (approximately 1 mM) correspond to the K_(i) values (TMA 1.4 mM and NMN 0.54 mM) which were measured for the basolateral uptake of TEA into rat proximal renal tubules. They clearly differ from the K_(i) values (TMA 70 mM and NMN 8.3 nM) which were determined for the luminal uptake of TEA.

EXAMPLE 4

Additional support for the basolateral location of OCT1 is provided by the K_(i) value (0.4 μM) which was obtained for the inhibition of OCT1-elicited uptake by 1,1'-diethyl-2,2'-cyanine iodide (decynium 22). In LLC-PK1 cells, a K_(i) value of 5.6 nM was determined for the transport of TEA across the luminal membrane whereas the K_(i) value for the transport of TEA across the basolateral membrane was estimated to be >0.1 μM. In order to characterize the OCT1 transport protein further, tests were carried out to determine whether MPP, which has an approximately 10 fold greater affinity than does TEA, is likewise transported by OCT1. Following the injection of 8 ng of OCT1 cRNA into oocytes, a specific uptake of ³ H-MPP was expressed which was inhibited by quinine. Similar V_(max) values for the expressed uptake of ¹⁴ C-TEA (148±4 pmol×oocytes⁻¹ ×h⁻¹) and ³ H-MPP (97±5 pmol×oocytes⁻¹ ×h⁻¹) were determined in a sample of oocytes. The existence of polyspecific cation transporters in liver cells has been reported. The uptake of MPP into cultured hepatocytes has recently been measured. In this context, it was found possible to inhibit approximately 90% of the MPP uptake using the same inhibitors which inhibit cation transport expressed by OCT1. The K_(i) values which were determined for MPP uptake in hepatocytes (O-methylisoprenaline 78 μM, MPP 13 μM, quinine 0.8 μM, decynium 22 0.23 μM and cyanine 863 0.10 μM) were virtually identical to the values which were obtained for the uptake of TEA by the OCT1 protein expressed by Xenopus oocytes. These data suggest that the OCT1 transport protein, or a highly homologous transport protein, is present in the plasma membrane of hepatocytes.

EXAMPLE 5

The nucleotide sequence and the amino acid sequence of OCT1 are depicted in FIG. 2a₁ (SEQ ID NO:4 and SEQ ID NO:1, respectively). Stop codons and a translation initiation site of the Kozak type (ACGCCATG) are to be found upstream of the open reading frame.

Analysis of the hydrophilicity/hydrophobicity of OCT1 identified 11 hydrophobic α-helical regions which probably traverse the membrane. The hydrophobicity/hydrophilicity indices are presented in FIG. 2b. The putative membrane-spanning regions are from 17 to 27 amino acids in length. They are linked to each other by one long, two medium-length and seven short hydrophilic regions. Since three potential N-glycolisation sites were predicted on the hydrophilic region between the first two membrane-traversing protein regions, the OCT1 orientation depicted in FIG. 2c has been proposed. The first hydrophilic region contains 14 negatively-charged amino acids which can be of importance for the binding of cations to OCT1.

EXAMPLE 6

Various rat tissues and some cell lines were analyzed for the localisation of OCT1 transport protein-specific mRNA using so-called Northern blots. For this purpose, the total RNA was isolated by the the guanidinium/phenol/chloroform method and the mRNA was purified by means of oligo(dT)-cellulose chromatography. The mRNA was fractionated by formaldehyde agarose gel electrophoresis, transferred to a Hybond-N membrane (Amersham) and then hybridized. For this, 5 μg of mRNA from the rat cells and from the cell line 293, and 1.5 μg of mRNA from the cell lines Caki-1 and LLC-PKI1, were loaded onto the formaldehyde agarose gel. The hybridization was carried out using a ³² P-labeled cDNA fragment of the novel DNA sequence from plasmid pOCT1 (nucleotides 285 to 1196 were used). The hybridization was carried out in hybridization solution (50% formamide, 5×SSPE, 5×Denhardt's solution, 0.5% SDS and 20 μg of salmon sperm DNA) at 42° C. for 18 hours. The membrane was washed in several steps to a final stringency of 0.25×SSPE, 0.1% SDS at 60° C. To display the results for cell line LLC-PK1, the film was exposed for 24 hours, and the film was exposed for 6 hours for the other tracks. An RNA standard (0.14 to 9.5 kilobase range from GIBCO/BRL) was used to determine the size of the RNA fragments. The sizes are given in FIG. 3.

The autoradiograph obtained from the Northern blot analysis is depicted in FIG. 3. Distinct bands at 1.9 kilobases and additional bands at 3.4 and 4.8 kilobases were observed in the case of the renal cortex, the renal medulla, the liver and the intestine. In cell line LLC-PK1, hybridization was only observed in the 3.4 kilobase region. By contrast, no OCT1 signals were observed in renal papilla, in skeletal muscle, in cardiac muscle, in the brain, or in the human embryonic kidney cell line 293 and in Caki-1 cells. Since cardiac and Caki-1 cells contain the extraneuronal noradrenalin transport protein, which is probably identical to the H⁺ cation antiport protein on luminal kidney membranes, the cation transport proteins in the basolateral and luminal membranes of the proximal renal tubules probably belong to different genetic families. In-situ hybridizations indicated that the OCT1 transport protein is expressed in the proximal renal tubules, in the epithelial cells of the liver and in the enterocytes of the small intestine.

The above examples demonstrate that a novel and unique protein has been cloned which plays an important role in eliminating cationic pharmaceuticals from the kidney and liver. This protein is presumably also involved in the absorption of cationic compounds from the intestine. Although cation transport and the excretion of pharmaceuticals have been intensively investigated for more than 30 years, it has only been possible in the past to make minor advances. The reason for this is that excretion of pharmaceuticals from the liver and kidneys includes transport across the basolateral and the luminal plasma membranes of the epithelial cells and that these transport processes are brought about by functionally different cation transport proteins. In addition to this, the possibility cannot be excluded that different cation transport proteins with similar substrate specificities are present in both the luminal and the basolateral renal membranes. One type of cation transport protein has been identified as a result of cloning the novel OCT1 transport protein. This has opened up many options for further research into the excretion of cationic pharmaceuticals.

EXAMPLE 7

Using the techniques described in the present application, it has been found possible to clone two human genes which are homologous with OCT1 and to sequence them completely or partially, respectively. The completely sequenced gene (HOCT1) is composed of 1885 bases (SEQ ID NO:5) and encodes a protein of 553 amino acids (SEQ ID NO:2). It is depicted in FIG. 2a₂. There is 78% identity between the amino acids of OCT1 and HOCT1. The second human gene (HOCT2) is composed of 1896 bases (SEQ ID NO:6) and encodes a protein of 555 amino acids (SEQ ID NO:3). The nucleotide sequence and the deduced amino acid sequence of HOCT2 are depicted in FIG. 2a₃. There is 68% identity between the amino acids of OCT1 and HOCT2.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the expression of OCT1 in Xenopus laevis oocytes. The rates of ¹⁴ -TEA uptake which are indicated represent the mean values of from 10 to 20 measurement s i standard deviation.

FIG. 1a shows a comparison of the NMN-inhibited uptake of ¹⁴ C-TEA which was observed after injecting water, 20 ng of rat kidney mRNA or 10 ng of OCT1 cRNA. The concentrations of ¹⁴ C-TEA and NMN in the incubation media were 200 μM and 10 mM, respectively.

FIG. 1b shows the rates of uptake of 200 μM ¹⁴ C-TEA after injecting different quantities of OCT1 cRNA. The curve was computed after fitting the Hill equation to the resulting data (n=1.9±0.2).

FIG. 1c shows the substrate-dependence of the ¹⁴ C-TEA uptake which was expressed following the injection of 3 ng of OCT1 cRNA per oocyte. The continuous line shows the total uptake which contains a saturable component and a linear component which was determined in control oocytes injected with water. The linear component was fitted by means of linear regression (dashed line, 30 fmol×h⁻¹ ×oocyte⁻¹ ×μM⁻¹). The saturable component was fitted using the Michaelis Menten equation (K_(m) 95±10 μM, V_(max) 81±5 pmol×h⁻¹ ×oocyte⁻¹). The unbroken line was computed by fitting to an equation which contains both components.

FIG. 1d shows the dependence on potential of the ¹⁴ C-TEA uptake in oocytes which were injected with 3 ng of OCT1 cRNA. The uptake of 95 μM ¹⁴ C-TEA was measured in the presence of the given concentrations of Na⁺, K⁺ and Ba²⁺. Under these conditions, the membrane potentials were between -40 and -60 mV (100 mM Na⁺ and 3 mM K⁺), from 0 to -10 mV (1 mM Na⁺ and 102 mM K⁺) and between -18 and -22 mV (100 mM Na⁺, 3 mM K⁺ and 10 mM Ba²⁺).

FIG. 1e shows the uptake of 95 μM ¹⁴ C-TEA in the presence and absence of proton gradients in oocytes which were injected with 3 ng of OCT1-cRNA. In order to prevent proton gradient-induced changes in the membrane potential, which would alter the uptake of ¹⁴ C-TEA, the measurements were carried out in the presence of 102 mM K⁺ and 1 mM Na⁺ in the incubation medium. This resulted in the membrane potential being brought to approximately 0 mV. pH measurements using microelectrodes indicated that the pH changed by less than 0.1 unit during the 30-minute uptake period.

FIG. 1f shows the inhibition of OCT1-elicited ¹⁴ C-TEA uptake by decynium 22 (∘), quinine (Δ), desipramine (□), procainamide ), O-methylisoprenaline (⋄) and tetramethylammonium (♦). The oocytes were injected with 5 ng of OCT1-cRNA and the measurements were carried out using 95 μM ¹⁴ C-TEA.

FIG. 2a₁ shows the nucleotide sequence of OCT1 (SEQ ID NO:4) and the amino acid sequence (SEQ ID NO:1) deduced from it. The putative transmembrane regions have been underlined and potential N-glycosylation sites of the NXT/S type are indicated by asterisks.

FIG. 2a₂ shows the nucleotide (SEQ ID NO:5) and amino acid (SEQ ID NO:2) sequences of an homologous human kidney gene (HOCT1). The gene fragment which is depicted encompasses 1885 bases and encodes 553 amino acids.

FIG. 2a₃ shows a nucleotide sequence (SEQ ID NO:6) and an amino acid sequence (SEQ ID NO:3) of a second homologous human kidney gene (HOCT2). The gene fragment depicted encompasses 1856 bases and encodes 555 amino acids.

FIG. 2b shows a Kyte/Doolittle hydrophobicity/hydrophilicity analysis of OCT1 using a window of 9 amino acids. The putative transmembrane regions are numbered 1 to 11.

FIG. 2c shows a diagrammatic representation of OCT1. The amino acid residues Arg, Lys and His are indicated by plus signs and the amino acid residues Glu and Asp by minus signs. Potential glycosylation sites in the first hydrophilic loop have been identified.

FIG. 3 shows the location of OCT1-specific mRNA in various rat tissues and in some cell lines.

    __________________________________________________________________________     #             SEQUENCE LISTING                                                    - -  - - (1) GENERAL INFORMATION:                                              - -    (iii) NUMBER OF SEQUENCES: 6                                            - -  - - (2) INFORMATION FOR SEQ ID NO:1:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 556 amino - #acids                                                 (B) TYPE: amino acid                                                           (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                  - -     (ii) MOLECULE TYPE: peptide                                            - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:1:                                - - Met Pro Thr Val Asp Asp Val Leu Glu Gln Va - #l Gly Glu Phe Gly         Trp                                                                              1               5   - #                10  - #                15               - - Phe Gln Lys Gln Ala Phe Leu Leu Leu Cys Le - #u Ile Ser Ala Ser Leu                   20      - #            25      - #            30                    - - Ala Pro Ile Tyr Val Gly Ile Val Phe Leu Gl - #y Phe Thr Pro Gly His               35          - #        40          - #        45                        - - Tyr Cys Gln Asn Pro Gly Val Ala Glu Leu Se - #r Gln Arg Cys Gly Trp           50              - #    55              - #    60                            - - Ser Gln Ala Glu Glu Leu Asn Tyr Thr Val Pr - #o Gly Leu Gly Pro Ser       65                  - #70                  - #75                  - #80         - - Asp Glu Ala Ser Phe Leu Ser Gln Cys Met Ar - #g Tyr Glu Val Asp Trp                       85  - #                90  - #                95                - - Asn Gln Ser Thr Leu Asp Cys Val Asp Pro Le - #u Ser Ser Leu Val Ala                   100      - #           105      - #           110                   - - Asn Arg Ser Gln Leu Pro Leu Gly Pro Cys Gl - #u His Gly Trp Val Tyr               115          - #       120          - #       125                       - - Asp Thr Pro Gly Ser Ser Ile Val Thr Glu Ph - #e Asn Leu Val Cys Gly           130              - #   135              - #   140                           - - Asp Ala Trp Lys Val Asp Leu Phe Gln Ser Cy - #s Val Asn Leu Gly Phe       145                 1 - #50                 1 - #55                 1 -       #60                                                                               - - Phe Leu Gly Ser Leu Val Val Gly Tyr Ile Al - #a Asp Arg Phe Gly         Arg                                                                                              165  - #               170  - #               175              - - Lys Leu Cys Leu Leu Val Thr Thr Leu Val Th - #r Ser Val Ser Gly Val                   180      - #           185      - #           190                   - - Leu Thr Ala Val Ala Pro Asp Tyr Thr Ser Me - #t Leu Leu Phe Arg Leu               195          - #       200          - #       205                       - - Leu Gln Gly Met Val Ser Lys Gly Ser Trp Va - #l Ser Gly Tyr Thr Leu           210              - #   215              - #   220                           - - Ile Thr Glu Phe Val Gly Ser Gly Tyr Arg Ar - #g Thr Thr Ala Ile Leu       225                 2 - #30                 2 - #35                 2 -       #40                                                                               - - Tyr Gln Met Ala Phe Thr Val Gly Leu Val Gl - #y Leu Ala Gly Val         Ala                                                                                              245  - #               250  - #               255              - - Tyr Ala Ile Pro Asp Trp Arg Trp Leu Gln Le - #u Ala Val Ser Leu Pro                   260      - #           265      - #           270                   - - Thr Phe Leu Phe Leu Leu Tyr Tyr Trp Phe Va - #l Pro Glu Ser Pro Arg               275          - #       280          - #       285                       - - Trp Leu Leu Ser Gln Lys Arg Thr Thr Arg Al - #a Val Arg Ile Met Glu           290              - #   295              - #   300                           - - Gln Ile Ala Gln Lys Asn Gly Lys Val Pro Pr - #o Ala Asp Leu Lys Met       305                 3 - #10                 3 - #15                 3 -       #20                                                                               - - Leu Cys Leu Glu Glu Asp Ala Ser Glu Lys Ar - #g Ser Pro Ser Phe         Ala                                                                                              325  - #               330  - #               335              - - Asp Leu Phe Arg Thr Pro Asn Leu Arg Lys Hi - #s Thr Val Ile Leu Met                   340      - #           345      - #           350                   - - Tyr Leu Trp Phe Ser Cys Ala Val Leu Tyr Gl - #n Gly Leu Ile Met His               355          - #       360          - #       365                       - - Val Gly Ala Thr Gly Ala Asn Leu Tyr Leu As - #p Phe Phe Tyr Ser Ser           370              - #   375              - #   380                           - - Leu Val Glu Phe Pro Ala Ala Phe Ile Ile Le - #u Val Thr Ile Asp Arg       385                 3 - #90                 3 - #95                 4 -       #00                                                                               - - Ile Gly Arg Ile Tyr Pro Ile Ala Ala Ser As - #n Leu Val Thr Gly         Ala                                                                                              405  - #               410  - #               415              - - Ala Cys Leu Leu Met Ile Phe Ile Pro His Gl - #u Leu His Trp Leu Asn                   420      - #           425      - #           430                   - - Val Thr Leu Ala Cys Leu Gly Arg Met Gly Al - #a Thr Ile Val Leu Glu               435          - #       440          - #       445                       - - Met Val Cys Leu Val Asn Ala Glu Leu Tyr Pr - #o Thr Phe Ile Arg Asn           450              - #   455              - #   460                           - - Leu Gly Met Met Val Cys Ser Ala Leu Cys As - #p Leu Gly Gly Ile Phe       465                 4 - #70                 4 - #75                 4 -       #80                                                                               - - Thr Pro Phe Met Val Phe Arg Leu Met Glu Va - #l Trp Gln Ala Leu         Pro                                                                                              485  - #               490  - #               495              - - Leu Ile Leu Phe Gly Val Leu Gly Leu Thr Al - #a Gly Ala Met Thr Leu                   500      - #           505      - #           510                   - - Leu Leu Pro Glu Thr Lys Gly Val Ala Leu Pr - #o Glu Thr Ile Glu Glu               515          - #       520          - #       525                       - - Ala Glu Asn Leu Gly Arg Arg Lys Ser Lys Al - #a Lys Glu Asn Thr Ile           530              - #   535              - #   540                           - - Tyr Leu Gln Val Gln Thr Gly Lys Ser Ser Se - #r Thr                       545                 5 - #50                 5 - #55                             - -  - - (2) INFORMATION FOR SEQ ID NO:2:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 553 amino - #acids                                                 (B) TYPE: amino acid                                                           (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                  - -     (ii) MOLECULE TYPE: peptide                                            - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:2:                                - - Met Pro Thr Val Asp Asp Ile Leu Glu Gln Va - #l Gly Glu Ser Gly Trp       1               5   - #                10  - #                15                - - Phe Gln Lys Gln Ala Phe Leu Ile Leu Cys Le - #u Leu Ser Ala Ala Phe                   20      - #            25      - #            30                    - - Ala Pro Ile Cys Val Gly Ile Val Phe Leu Gl - #y Phe Thr Pro Asp His               35          - #        40          - #        45                        - - His Cys Gln Ser Pro Gly Val Ala Glu Leu Se - #r Gln Arg Cys Gly Trp           50              - #    55              - #    60                            - - Ser Pro Ala Glu Glu Leu Asn Tyr Thr Val Pr - #o Gly Leu Gly Pro Ala       65                  - #70                  - #75                  - #80         - - Gly Glu Ala Phe Leu Gly Gln Cys Arg Arg Ty - #r Glu Val Asp Trp Asn                       85  - #                90  - #                95                - - Gln Ser Ala Leu Ser Cys Val Asp Pro Leu Al - #a Ser Leu Ala Thr Asn                   100      - #           105      - #           110                   - - Arg Ser His Leu Pro Leu Gly Pro Cys Gln As - #p Gly Trp Val Tyr Asp               115          - #       120          - #       125                       - - Thr Pro Gly Ser Ser Ile Val Thr Glu Phe As - #n Leu Val Cys Ala Asp           130              - #   135              - #   140                           - - Ser Trp Lys Leu Asp Leu Phe Gln Ser Cys Le - #u Asn Ala Gly Phe Phe       145                 1 - #50                 1 - #55                 1 -       #60                                                                               - - Phe Gly Ser Leu Gly Val Gly Tyr Phe Ala As - #p Arg Phe Gly Arg         Lys                                                                                              165  - #               170  - #               175              - - Leu Cys Leu Leu Gly Thr Val Leu Val Asn Al - #a Val Ser Gly Val Leu                   180      - #           185      - #           190                   - - Met Ala Phe Ser Pro Asn Tyr Met Ser Met Le - #u Leu Phe Arg Leu Leu               195          - #       200          - #       205                       - - Gln Gly Leu Val Ser Lys Gly Asn Trp Met Al - #a Gly Tyr Thr Leu Ile           210              - #   215              - #   220                           - - Thr Glu Phe Val Gly Ser Gly Ser Arg Arg Th - #r Val Ala Ile Met Tyr       225                 2 - #30                 2 - #35                 2 -       #40                                                                               - - Gln Met Ala Phe Thr Val Gly Leu Val Ala Le - #u Thr Gly Leu Ala         Tyr                                                                                              245  - #               250  - #               255              - - Ala Leu Pro His Trp Arg Trp Leu Gln Leu Al - #a Val Ser Leu Pro Thr                   260      - #           265      - #           270                   - - Phe Leu Phe Leu Leu Tyr Tyr Trp Cys Val Pr - #o Glu Ser Pro Arg Trp               275          - #       280          - #       285                       - - Leu Leu Ser Gln Lys Arg Asn Thr Glu Ala Il - #e Lys Ile Met Asp His           290              - #   295              - #   300                           - - Ile Ala Gln Lys Asn Gly Lys Leu Pro Pro Al - #a Asp Leu Lys Met Leu       305                 3 - #10                 3 - #15                 3 -       #20                                                                               - - Ser Leu Glu Glu Asp Val Thr Glu Lys Leu Se - #r Pro Ser Phe Ala         Asp                                                                                              325  - #               330  - #               335              - - Leu Phe Arg Thr Pro Arg Leu Arg Lys Arg Th - #r Phe Ile Leu Met Tyr                   340      - #           345      - #           350                   - - Leu Trp Phe Thr Asp Ser Val Leu Tyr Gln Gl - #y Leu Ile Leu His Met               355          - #       360          - #       365                       - - Gly Ala Thr Ser Gly Asn Leu Tyr Leu Asp Ph - #e Leu Tyr Ser Ala Leu           370              - #   375              - #   380                           - - Val Glu Ile Pro Gly Ala Phe Ile Ala Leu Il - #e Thr Ile Asp Arg Val       385                 3 - #90                 3 - #95                 4 -       #00                                                                               - - Gly Arg Ile Tyr Pro Met Ala Val Ser Asn Le - #u Leu Ala Gly Ala         Ala                                                                                              405  - #               410  - #               415              - - Cys Leu Val Ile Phe Ile Ser Pro Asp Leu Hi - #s Trp Leu Asn Ile Ile                   420      - #           425      - #           430                   - - Ile Met Cys Val Gly Arg Met Gly Ile Thr Il - #e Ala Ile Gln Met Ile               435          - #       440          - #       445                       - - Cys Leu Val Asn Ala Glu Leu Tyr Pro Thr Ph - #e Val Arg Asn Leu Arg           450              - #   455              - #   460                           - - Val Met Val Cys Ser Ser Leu Cys Asp Ile Gl - #y Gly Ile Ile Thr Pro       465                 4 - #70                 4 - #75                 4 -       #80                                                                               - - Phe Ile Val Phe Arg Leu Arg Glu Val Trp Gl - #n Ala Leu Pro Leu         Ile                                                                                              485  - #               490  - #               495              - - Leu Phe Ala Val Leu Gly Leu Leu Ala Ala Gl - #y Val Thr Leu Leu Leu                   500      - #           505      - #           510                   - - Pro Glu Thr Lys Gly Asp Ala Leu Pro Glu Th - #r Met Lys Asp Ala Glu               515          - #       520          - #       525                       - - Asn Leu Gly Arg Lys Ala Lys Pro Lys Glu As - #n Thr Ile Tyr Leu Lys           530              - #   535              - #   540                           - - Val Gln Thr Ser Glu Pro Ser Gly Thr                                       545                 5 - #50                                                     - -  - - (2) INFORMATION FOR SEQ ID NO:3:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 555 amino - #acids                                                 (B) TYPE: amino acid                                                           (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                  - -     (ii) MOLECULE TYPE: peptide                                            - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:3:                                - - Met Pro Thr Thr Val Asp Asp Val Leu Glu Hi - #s Gly Gly Glu Phe His       1               5   - #                10  - #                15                - - Phe Phe Gln Lys Gln Met Phe Phe Leu Leu Al - #a Leu Leu Ser Ala Thr                   20      - #            25      - #            30                    - - Phe Ala Pro Ile Tyr Val Gly Ile Val Phe Le - #u Gly Phe Thr Pro Asp               35          - #        40          - #        45                        - - His Arg Cys Arg Ser Pro Gly Val Ala Glu Le - #u Ser Leu Arg Cys Gly           50              - #    55              - #    60                            - - Trp Ser Pro Ala Glu Glu Leu Asn Tyr Thr Va - #l Pro Gly Pro Gly Pro       65                  - #70                  - #75                  - #80         - - Ala Gly Glu Ala Ser Pro Arg Gln Cys Arg Ar - #g Tyr Glu Val Asp Trp                       85  - #                90  - #                95                - - Asn Gln Ser Thr Phe Asp Cys Val Asp Pro Le - #u Ala Ser Leu Asp Thr                   100      - #           105      - #           110                   - - Asn Arg Ser Arg Leu Pro Leu Gly Pro Cys Ar - #g Asp Gly Trp Val Tyr               115          - #       120          - #       125                       - - Glu Thr Pro Gly Ser Ser Ile Val Thr Glu Ph - #e Asn Leu Val Cys Ala           130              - #   135              - #   140                           - - Asn Ser Trp Met Leu Asp Leu Phe Gln Ser Se - #r Val Asn Val Gly Phe       145                 1 - #50                 1 - #55                 1 -       #60                                                                               - - Phe Ile Gly Ser Met Ser Ile Gly Tyr Ile Al - #a Asp Arg Phe Gly         Arg                                                                                              165  - #               170  - #               175              - - Lys Leu Cys Leu Leu Thr Thr Val Leu Ile As - #n Ala Ala Ala Gly Val                   180      - #           185      - #           190                   - - Leu Met Ala Ile Ser Pro Thr Tyr Thr Trp Me - #t Leu Ile Phe Arg Leu               195          - #       200          - #       205                       - - Ile Gln Gly Leu Val Ser Lys Ala Gly Trp Le - #u Ile Gly Tyr Ile Leu           210              - #   215              - #   220                           - - Ile Thr Glu Phe Val Gly Gly Arg Tyr Arg Ar - #g Thr Val Gly Ile Phe       225                 2 - #30                 2 - #35                 2 -       #40                                                                               - - Tyr Gln Val Ala Tyr Thr Val Gly Leu Leu Va - #l Leu Ala Gly Val         Ala                                                                                              245  - #               250  - #               255              - - Tyr Ala Leu Pro His Trp Arg Trp Leu Gln Ph - #e Thr Val Ala Leu Pro                   260      - #           265      - #           270                   - - Asn Phe Phe Phe Leu Leu Tyr Tyr Trp Cys Il - #e Pro Glu Ser Pro Arg               275          - #       280          - #       285                       - - Trp Leu Ile Ser Gln Asn Lys Asn Ala Glu Al - #a Met Arg Ile Ile Lys           290              - #   295              - #   300                           - - His Ile Ala Lys Lys Asn Gly Lys Ser Leu Pr - #o Ala Ser Leu Gln Arg       305                 3 - #10                 3 - #15                 3 -       #20                                                                               - - Leu Arg Leu Glu Glu Glu Thr Gly Lys Lys Le - #u Asn Pro Ser Phe         Leu                                                                                              325  - #               330  - #               335              - - Asp Leu Val Arg Thr Pro Gln Ile Arg Lys Hi - #s Thr Met Ile Leu Met                   340      - #           345      - #           350                   - - Tyr Asn Trp Phe Thr Ser Ser Val Leu Tyr Gl - #n Gly Leu Ile Met His               355          - #       360          - #       365                       - - Met Gly Leu Ala Gly Asp Asn Ile Tyr Leu As - #p Phe Phe Tyr Ser Ala           370              - #   375              - #   380                           - - Leu Val Glu Phe Pro Ala Ala Phe Met Ile Il - #e Leu Ile Ile Asp Arg       385                 3 - #90                 3 - #95                 4 -       #00                                                                               - - Ile Gly Arg Arg Tyr Pro Trp Ala Ala Ser As - #n Met Val Ala Gly         Ala                                                                                              405  - #               410  - #               415              - - Ala Cys Leu Ala Ser Val Phe Ile Pro Gly As - #p Leu Gln Trp Leu Lys                   420      - #           425      - #           430                   - - Ile Ile Ile Ser Cys Leu Gly Arg Met Gly Il - #e Thr Met Ala Tyr Glu               435          - #       440          - #       445                       - - Ile Val Cys Leu Val Asn Ala Glu Leu Tyr Pr - #o Thr Phe Ile Arg Asn           450              - #   455              - #   460                           - - Leu Gly Val His Ile Cys Ser Ser Met Cys As - #p Ile Gly Gly Ile Ile       465                 4 - #70                 4 - #75                 4 -       #80                                                                               - - Thr Pro Phe Leu Val Tyr Arg Leu Thr Asn Il - #e Trp Leu Glu Leu         Pro                                                                                              485  - #               490  - #               495              - - Leu Met Val Phe Gly Val Leu Gly Leu Val Al - #a Gly Gly Leu Ala Leu                   500      - #           505      - #           510                   - - Leu Leu Pro Glu Thr Lys Gly Lys Ala Leu Pr - #o Glu Thr Ile Glu Glu               515          - #       520          - #       525                       - - Ala Glu Asn Met Gln Arg Pro Arg Lys Asn Ly - #s Glu Lys Met Ile Tyr           530              - #   535              - #   540                           - - Leu Gln Val Gln Lys Leu Asp Ile Pro Leu As - #n                           545                 5 - #50                 5 - #55                             - -  - - (2) INFORMATION FOR SEQ ID NO:4:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 1882 base - #pairs                                                 (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                  - -     (ii) MOLECULE TYPE: DNA (genomic)                                      - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:4:                                - - GCAGGCCTGG CTAAACTGGT GAGGGCCCTA CCCAGCCATG CCCACCGTGG AT -              #GATGTCCT     60                                                                  - - GGAGCAAGTT GGAGAGTTTG GCTGGTTCCA GAAACAAGCC TTCCTGTTGC TA -             #TGCCTGAT    120                                                                  - - CTCAGCTTCT TTAGCTCCCA TCTATGTGGG CATCGTCTTC CTGGGCTTCA CC -             #CCTGGACA    180                                                                  - - TTATTGCCAG AATCCTGGGG TGGCTGAGCT GAGCCAGCGG TGTGGCTGGA GC -             #CAGGCAGA    240                                                                  - - GGAGCTGAAC TACACTGTGC CGGGCCTGGG ACCTTCGGAC GAGGCCTCCT TC -             #CTCAGCCA    300                                                                  - - GTGCATGAGG TATGAGGTGG ACTGGAACCA GAGCACCCTT GACTGTGTGG AC -             #CCACTGTC    360                                                                  - - CAGCCTGGTT GCCAACAGGA GTCAGTTGCC ATTGGGCCCC TGCGAGCATG GC -             #TGGGTATA    420                                                                  - - CGACACTCCC GGCTCCTCCA TCGTCACTGA GTTTAACCTG GTGTGTGGAG AC -             #GCCTGGAA    480                                                                  - - AGTGGACCTT TTTCAGTCCT GTGTGAACTT GGGCTTCTTC CTGGGCTCCC TG -             #GTTGTGGG    540                                                                  - - TTACATTGCA GACAGGTTTG GCCGTAAGCT CTGTCTCTTG GTGACCACGC TG -             #GTCACATC    600                                                                  - - TGTGTCCGGT GTGCTAACAG CGGTGGCCCC AGACTATACA TCCATGTTGC TC -             #TTTCGCCT    660                                                                  - - GCTGCAGGGC ATGGTCAGCA AGGGCAGCTG GGTGTCCGGC TATACCTTGA TC -             #ACAGAGTT    720                                                                  - - TGTCGGCTCT GGCTACAGGA GAACGACGGC CATTTTGTAC CAGATGGCCT TC -             #ACAGTGGG    780                                                                  - - GCTAGTGGGG CTTGCCGGGG TGGCCTATGC CATTCCAGAC TGGCGCTGGC TC -             #CAGCTAGC    840                                                                  - - TGTGTCCCTG CCTACCTTCC TCTTCCTGCT GTATTACTGG TTTGTCCCAG AA -             #TCCCCCCG    900                                                                  - - GTGGCTGTTG TCCCAGAAGA GAACCACGCG AGCTGTCAGG ATAATGGAGC AA -             #ATTGCACA    960                                                                  - - GAAGAACGGG AAGGTGCCTC CTGCTGACCT GAAGATGCTC TGCCTTGAGG AG -             #GATGCCTC   1020                                                                  - - AGAAAAGCGA AGTCCTTCGT TTGCCGACCT GTTCCGCACT CCCAACCTGA GG -             #AAGCACAC   1080                                                                  - - CGTCATCCTG ATGTATCTAT GGTTCTCTTG TGCTGTGCTG TACCAGGGTC TC -             #ATCATGCA   1140                                                                  - - CGTGGGAGCC ACAGGGGCCA ACCTCTACCT GGACTTCTTT TATTCTTCTC TG -             #GTGGAATT   1200                                                                  - - CCCCGCGGCC TTCATCATCC TGGTCACCAT TGACCGCATT GGCCGCATCT AC -             #CCAATAGC   1260                                                                  - - GGCCTCGAAT CTGGTGACGG GGGCAGCCTG CCTCCTCATG ATCTTTATCC CG -             #CATGAGCT   1320                                                                  - - GCACTGGTTG AACGTTACCC TCGCCTGTCT TGGCCGTATG GGGGCCACCA TT -             #GTGCTGCA   1380                                                                  - - GATGGTCTGC CTGGTGAACG CTGAGCTGTA CCCTACATTC ATCAGGAATC TT -             #GGGATGAT   1440                                                                  - - GGATTGCTCT GCCCTGTGTG ACCTGGGTGG GATCTTCACC CCCTTCATGG TG -             #TTCAGGCT   1500                                                                  - - GATGGAAGTT TGGCAAGCCC TGCCCCTCAT TTTGTTTGGG GTTTTGGGCC TG -             #ACTGCTGG   1560                                                                  - - GGCCATGACT CTTCTTCTCC CAGAGACCAA GGGTGTGGCT TTGCCTGAGA CT -             #ATTGAAGA   1620                                                                  - - AGCAGAGAAC CTGGGGAGGA GGAAATCAAA GGCCAAAGAA AACACGATTT AC -             #CTTCAGGT   1680                                                                  - - CCAAACAGGC AAGTCCTCAA GTACCTGACA GGGATGCTGT GCCAGGAGCT GA -             #GTGGCAGA   1740                                                                  - - GAGAAAGGAG GACTTGCCAC TTGGAGGATT CCCAGAAGCC TTTGCCTTTC CA -             #GACTCTTG   1800                                                                  - - TATATATGCA CCAGGTTCCA AATGAACTAC CAACCTTAAA GACTTTTCTG AA -             #AGCCCAAA   1860                                                                  - - AAAAAAAAAA AAAAAAAAAA AA           - #                  - #                    1882                                                                      - -  - - (2) INFORMATION FOR SEQ ID NO:5:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 1885 base - #pairs                                                 (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                  - -     (ii) MOLECULE TYPE: DNA (genomic)                                      - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:5:                                - - GAGGGAGACA TTGCACCTGG CCACTGCAGC CCAGAGCAGG TCTGGCCACG GC -              #CATGAGCA     60                                                                  - - TGCTGAGCCA TCATGCCCAC CGTGGATGAC ATTCTGGAGC AGGTTGGGGA GT -             #CTGGCTGG    120                                                                  - - TTCCAGAAGC AAGCCTTCCT CATCTTATGC CTGCTGTCGG CTGCCTTTGC GC -             #CCATCTGT    180                                                                  - - GTGGGCATCG TCTTCCTGGG TTTCACACCT GACCACCACT GCCAGAGCCC TG -             #GGGTGGCT    240                                                                  - - GAGCTGAGCC AGCGCTGTGG CTGGAGCCCT GCGGAGGAGC TGAACTATAC AG -             #TGCCAGGC    300                                                                  - - CTGGGGCCCG CGGGCGAGGC CTTCCTTGGC CAGTGCAGGC GCTATGAAGT GG -             #ACTGGAAC    360                                                                  - - CAGAGCGCCC TCAGCTGTGT AGACCCCCTG GCTAGCCTGG CCACCAACAG GA -             #GCCACCTG    420                                                                  - - CCGCTGGGTC CCTGCCAGGA TGGCTGGGTG TATGACACGC CCGGCTCTTC CA -             #TCGTCACT    480                                                                  - - GAGTTCAACC TGGTGTGTGC TGACTCCTGG AAGCTGGACC TCTTTCAGTC CT -             #GTTTGAAT    540                                                                  - - GCGGGCTTCT TCTTTGGCTC TCTCGGTGTT GGCTACTTTG CAGACAGGTT TG -             #GCCGTAAG    600                                                                  - - CTGTGTCTCC TGGGAACTGT GCTGGTCAAC GCGGTGTCGG GCGTGCTCAT GG -             #CCTTCTCG    660                                                                  - - CCCAACTACA TGTCCATGCT GCTCTTCCGC CTGCTGCAGG GCCTGGTCAG CA -             #AGGGCAAC    720                                                                  - - TGGATGGCTG GCTACACCCT AATCACAGAA TTTGTTGGCT CGGGCTCCAG AA -             #GAACGGTG    780                                                                  - - GCGATCATGT ACCAGATGGC CTTCACGGTG GGGCTGGTGG CGCTTACCGG GC -             #TGGCCTAC    840                                                                  - - GCCCTGCCTC ACTGGCGCTG GCTGCAGCTG GCAGTCTCCC TGCCCACCTT CC -             #TCTTCCTG    900                                                                  - - CTCTACTACT GGTGTGTGCC GGAGTCCCCT CGGTGGCTGT TATCACAAAA AA -             #GAAACACT    960                                                                  - - GAAGCAATAA AGATAATGGA CCACATCGCT CAAAAGAATG GGAAGTTGCC TC -             #CTGCTGAT   1020                                                                  - - TTAAAGATGC TTTCCCTCGA AGAGGATGTC ACCGAAAAGC TGAGCCCTTC AT -             #TTGCAGAC   1080                                                                  - - CTGTTCCGCA CGCCGCGCCT GAGGAAGCGC ACCTTCATCC TGATGTACCT GT -             #GGTTCACG   1140                                                                  - - GACTCTGTGC TCTATCAGGG GCTCATCCTG CACATGGGCG CCACCAGCGG GA -             #ACCTCTAC   1200                                                                  - - CTGGATTTCC TTTACTCCGC TCTGGTCGAA ATCCCGGGGG CCTTCATAGC CC -             #TCATCACC   1260                                                                  - - ATTGACCGCG TGGGCCGCAT CTACCCCATG GCCGTGTCAA ATTTGTTGGC GG -             #GGGCAGCC   1320                                                                  - - TGCCTCGTCA TTTTTATCTC ACCTGACCTG CACTGGTTAA ACATCATAAT CA -             #TGTGTGTT   1380                                                                  - - GGCCGAATGG GAATCACCAT TGCAATACAA ATGATCTGCC TGGTGAATGC TG -             #AGCTGTAC   1440                                                                  - - CCCACATTCG TCAGGAACCT CAGAGTGATG GTGTGTTCCT CCCTGTGTGA CA -             #TAGGTGGG   1500                                                                  - - ATAATCACCC CCTTCATAGT CTTCAGGCTG AGGGAGGTCT GGCAAGCCTT GC -             #CCCTCATT   1560                                                                  - - TTGTTTGCGG TGTTGGGCCT GCTTGCCGCG GGAGTGACGC TACTTCTTCC AG -             #AGACCAAG   1620                                                                  - - GGGGACGCTT TGCCAGAGAC CATGAAGGAC GCCGAGAACC TTGGGAGAAA AG -             #CAAAGCCC   1680                                                                  - - AAAGAAAACA CGATTTACCT TAAGGTCCAA ACCTCAGAAC CCTCGGGCAC CT -             #GAGAGAGA   1740                                                                  - - TGTTTTGCGG CGATGTCGTG TTGGAGGGAT GAAGATGGAG TTATCCTCTG CA -             #GAAATTCC   1800                                                                  - - TAGACGCCTT CACTTCTCTG TATTCTTCCT CATACTTGCC TACCCCCAAA TT -             #AATATCAG   1860                                                                  - - TCCTAAAGAA AAAAAAAAAA AAAAA          - #                  - #                  1885                                                                      - -  - - (2) INFORMATION FOR SEQ ID NO:6:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 1896 base - #pairs                                                 (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                  - -     (ii) MOLECULE TYPE: DNA (genomic)                                      - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:6:                                - - GGCCCTGCCC TGAAGGCTGG TCACTTGCAG AGGTAAACTC CCCTCTTTGA CT -              #TCTGGCCA     60                                                                  - - GGGTTTGTGC TGAGCTGGCT GCAGCCGCTC TCAGCCTCGC TCCGGGCACG TC -             #GGGCAGCC    120                                                                  - - TCGGGCCCTC CTGCCTGCAG GATCATGCCC ACCACCGTGG ACGATGTCCT GG -             #AGCATGGA    180                                                                  - - GGGGAGTTTC ACTTTTTCCA GAAGCAAATG TTTTTCCTCT TGGCTCTGCT CT -             #CGGCTACC    240                                                                  - - TTCGCGCCCA TCTACGTGGG CATCGTCTTC CTGGGCTTCA CCCCTGACCA CC -             #GCTGCCGG    300                                                                  - - AGCCCCGGAG TGGCCGAGCT GAGTCTGCGC TGCGGCTGGA GTCCTGCAGA GG -             #AACTGAAC    360                                                                  - - TACACGGTGC CGGGCCCAGG ACCTGCGGGC GAAGCCTCCC CAAGACAGTG TA -             #GGCGCTAC    420                                                                  - - GAGGTGGACT GGAACCAGAG CACCTTTGAC TGCGTGGACC CCCTGGCCAG CC -             #TGGACACC    480                                                                  - - AACAGGAGCC GCCTGCCACT GGGCCCCTGC CGGGACGGCT GGGTGTACGA GA -             #CGCCTGGC    540                                                                  - - TCGTCCATCG TCACCGAGTT TAACCTGGTA TGTGCCAACT CCTGGATGTT GG -             #ACCTATTC    600                                                                  - - CAGTCATCAG TGAATGTAGG ATTCTTTATT GGCTCTATGA GTATCGGCTA CA -             #TAGCAGAC    660                                                                  - - AGGTTTGGCC GTAAGCTCTG CCTCCTAACT ACAGTCCTCA TAAATGCTGC AG -             #CTGGAGTT    720                                                                  - - CTCATGGCCA TTTCCCCAAC CTATACGTGG ATGTTAATTT TTCGCTTAAT CC -             #AAGGACTG    780                                                                  - - GTCAGCAAAG CAGGCTGGTT AATAGGCTAC ATCCTGATTA CAGAATTTGT TG -             #GGGGGAGA    840                                                                  - - TATCGGAGAA CAGTGGGGAT TTTTTACCAA GTTGCCTATA CAGTTGGGCT CC -             #TGGTGCTA    900                                                                  - - GCTGGGGTGG CTTACGCACT TCCTCACTGG AGGTGGTTGC AGTTCACAGT TG -             #CTCTGCCC    960                                                                  - - AACTTCTTCT TCTTGCTCTA TTACTGGTGC ATACCTGAGT CTCCCAGGTG GC -             #TGATCTCC   1020                                                                  - - CAGAATAAGA ATGCTGAAGC CATGAGAATC ATTAAGCACA TCGCAAAGAA AA -             #ATGGAAAA   1080                                                                  - - TCTCTACCCG CCTCCCTTCA GCGCCTGAGA CTTGAAGAGG AAACTGGCAA GA -             #AATTGAAC   1140                                                                  - - CCTTCATTTC TTGACTTGGT CAGAACTCCT CAGATAAGGA AACATACTAT GA -             #TATTGATG   1200                                                                  - - TACAACTGGT TCACGAGCTC TGTGCTCTAC CAGGGCCTCA TCATGCACAT GG -             #GCCTTGCA   1260                                                                  - - GGTGACAATA TCTACCTGGA TTTCTTCTAC TCTGCCCTGG TTGAATTCCC AG -             #CTGCCTTC   1320                                                                  - - ATGATCATCC TCATTATCGA CCGCATCGGA CGCCGTTACC CTTGGGCTGC AT -             #CAAATATG   1380                                                                  - - GTTGCAGGGG CAGCCTGTCT GGCCTCAGTT TTTATACCTG GTGATCTACA AT -             #GGCTAAAA   1440                                                                  - - ATTATTATCT CATGCTTGGG AAGAATGGGG ATCACAATGG CCTATGAGAT AG -             #TCTGCCTG   1500                                                                  - - GTCAATGCTG AGCTGTACCC CACATTCATT AGGAATCTTG GCGTCCACAT CT -             #GTTCCTCA   1560                                                                  - - ATGTGTGACA TTGGTGGCAT CATCACGCCA TTCCTGGTCT ACCGGCTCAC TA -             #ACATCTGG   1620                                                                  - - CTTGAGCTCC CGCTGATGGT TTTCGGCGTA CTTGGCTTGG TTGCTGGAGG TC -             #TGGTGCTG   1680                                                                  - - TTGCTTCCAG AAACTAAAGG GAAAGCTTTG CCTGAGACCA TCGAGGAAGC CG -             #AAAATATG   1740                                                                  - - CAAAGACCAA GAAAAAATAA AGAAAAGATG ATTTACCTCC AAGTTCAGAA AC -             #TAGACATT   1800                                                                  - - CCATTGAACT AAGAAGAGAG ACCGTTGCTG CTGTCATGAC CTAGCTTTAT GG -             #CAGCAAGA   1860                                                                  - - CCAAAAGTAG AAATCCCTGC ACTCATCACA AAGCCC      - #                        - #     1896                                                                   __________________________________________________________________________ 

What is claimed is:
 1. An isolated and purified transport protein that transports either or both of cationic xenobiotics and pharmaceuticals from blood into liver or kidney epithelial cells, or transports either or both of cationic xenobiotics and pharmaceuticals from an intestine into the blood circulation, wherein said transport protein comprises an amino acid sequence depicted in FIG. 2a₁ (SEQ. ID NO: 1), 2a₂ (SEQ ID NO: 2), or 2a₃ (SEQ ID NO: 3).
 2. A method for altering the renal and biliary excretion or intestinal absorption of a biologically active compound comprising attaching to said biologically active compound a cationic signal molecule, wherein said cationic signal molecule is transported by the transport protein as claimed in claim
 1. 3. A method for decreasing the nephrotoxicity of either or both of cationic pharmaceuticals and xenobiotics comprising preventing uptake of said cationic pharmaceuticals and xenobiotics into renal tubule cells by exposing said cells to antibodies against the transport protein as claimed in claim
 1. 